Assessment of subventricular zone irradiation in glioblastoma patients

Glioblastoma (GBM) is the most aggressive primary brain tumor in adults, with near-universal recurrence despite multimodality treatment. Increasing evidence suggests that the subventricular zone (SVZ), a major neural stem cell niche, may contribute to tumor aggressiveness, recurrence, and therapeutic resistance. However, the clinical significance of incidental SVZ irradiation remains controversial.

This prospective analytical study included 28 consecutive patients with histologically confirmed GBM treated uniformly with maximal safe resection followed by temozolomide-based chemoradiation using IMRT/VMAT. Ipsilateral, contralateral, and bilateral SVZs were retrospectively contoured, and dosimetric parameters were extracted. Survival outcomes were correlated with SVZ contact and radiation dose. The primary endpoints were overall survival (OS) and progression-free survival (PFS).

With a median follow-up of 14.5 months, median OS and PFS were 13 months and 6.5 months, respectively. Tumors contacting the SVZ were associated with inferior OS (7 vs 15 months; p = 0.044) and shorter PFS. On univariate analysis, SVZ contact was associated with worse survival (HR 4.04). Among patients with SVZ-contacting tumors, a higher ipsilateral SVZ dose (≥52.14 Gy) showed a trend toward improved OS (p = 0.04). However, given the limited number of events, these findings should be interpreted with caution.

SVZ contact appears to identify a higher-risk subgroup of GBM patients. Higher incidental irradiation of the ipsilateral SVZ may be associated with improved survival; however, due to the small sample size and limited events, these findings are exploratory and hypothesis-generating. Larger prospective studies are required before clinical implementation.